1. Field of the Invention
The present invention relates to a rotary connector attached to a steering shaft of an automobile or the like and adapted to effect electrical connection between electric devices provided in a steering wheel and a vehicle body.
2. Description of the Related Art
Hitherto, a rotary connector has been proposed which electrically connects an electric device provided in a steering wheel with an electric device provided in a vehicle body.
A rotary connector, which makes it possible to establish electrical connection between an electric device provided in a steering wheel, which is a rotary member, and an electric device provided in a vehicle body, which is a stationary member, accommodates a flexible electric cable or an optical fiber (which will be hereinafter generally referred to as xe2x80x9cflexible cablexe2x80x9d) wound between a rotor portion rotated by the steering wheel and a case constituting a stator portion, one end of the cable being fastened to the rotor portion, the other end thereof being fastened to the stator portion, electrical connection between the electric devices being made possible by utilizing winding and rewinding of the flexible cable.
A conventional rotary connector will be described with reference to drawings.
FIG. 8 is an exploded perspective view of a conventional rotary connector; FIG. 9 is a sectional view of the conventional rotary connector; FIG. 10 is an enlarged sectional view of portion A of FIG. 9; FIG. 11 is a perspective view of an upper rotor portion and a lead block in the conventional rotary connector; FIG. 12 is a perspective view of the lead block of the conventional rotary connector; and FIG. 13 is a perspective view of a lower rotor portion of the conventional rotary connector.
First, as shown in FIGS. 8 and 9, this rotary connector 100 generally comprises an upper rotor member 11, a lower rotor member 12, a cable accommodating portion 13 and a lower cover 14, which are connected concentrically and rotatably, and a flexible cable 15 accommodated and wound in the space between the upper and lower rotor members 11 and 12 and the cable accommodating portion 13 and the lower cover 14, both ends of the flexible cable 15 being electrically led out indirectly to the exterior of the cable accommodating portion 13, etc. through an inner lead block 16 and an outer lead block 17. The inner lead block 16 is locked to the outer edge portion of the upper rotor member 11, and the outer lead block 17 is locked to the outer edge portion of the lower cover 14.
And, the upper rotor member 11 and the lower rotor member 12 are combined to form an integral unit serving as a movable member housing, and the cable accommodating portion 13 and the lower cover 14 are combined to form an integral unit serving as a stationary member housing. When the movable member housing is rotated clockwise or counterclockwise, the flexible cable 15 is wound or rewound in the space.
In this rotary connector 100, the upper and lower rotor members 11 and 12 forming the movable member housing and the cable accommodating portion 13 and the lower cover 14 forming the stationary member housing are engaged with each other relatively loosely, and a relatively large clearance is formed in the engagement portion. Due to the play between the movable member housing and the stator member housing owing to the clearance in this engagement portion, the stability in the rotation of the rotary connector 100 is maintained.
In this rotary connector 100, generally constructed as described above, the stationary member housing consisting of the cable accommodating portion 13 and the lower cover 14 is secured to a vehicle body (not shown), and the movable member housing consisting of the upper rotor member 11 and the lower rotor member 12 is secured to a hub (not shown) of a steering shaft. Further, both ends of the flexible cable 15 are connected to electric devices provided in the vehicle body and the steering wheel through connectors 18 and 19, whereby the rotary connector is used as an electrical connection means for a motor-vehicle-mounted air back system, a horn circuit, etc.
Next, the upper rotor member 11 and the inner lead block 16 of the conventional rotary connector 100 will be described.
As shown in FIG. 11, the upper rotor member 11 of the rotary connector 100 is formed of a synthetic resin material, molded, has a substantially ring-like configuration, and comprises a small diameter cylindrical portion 11b having a round center hole 11a at its center, an intermediate diameter cylindrical portion 11c outwardly (upwardly) connected to the small diameter cylindrical portion 11b, a large diameter cylindrical portion 11d outwardly (upwardly) connected to the intermediate diameter cylindrical portion 11c, and a circular flange portion 11e outwardly protruding from the upper end portion of the large diameter cylindrical portion 11d. 
Further, at a predetermined position of a flat portion 11f between the intermediate diameter cylindrical portion 11c and the large diameter cylindrical portion 11d, there is provided a substantially box-shaped accommodating portion 11g which protrudes outwardly (upwardly), and a substantially rectangular opening 11n is provided in a part of an upper surface 11p of this accommodating portion 11g. To achieve a uniform balance in weight in order that the upper rotor member 11 may rotate in a stable manner, this accommodating portion 11g is thin-walled and light in weight. Further, on the inner wall of the small diameter cylindrical portion 11b, there are provided a plurality of (e.g., four) engagement portions 11h which are substantially triangular-pyramid-shaped, a plurality of (e.g., two) prism-shaped protrusions which are parallel with the axis, and a substantially rectangular recess 11j. 
The upper surface 11k of each engagement portion 11h (See FIG. 10) is formed as a plane orthogonal to the axis of the movable member housing, and the lower surface 11m there is inclined so as to make a predetermined angle with respect to the axis.
As shown in FIG. 12, the inner lead block 16 of the rotary connector 100 is formed of a synthetic resin material, shaped, and comprises a joint base 16a having a substantially U-shaped section, a joint cover 16b arranged so as to close the open surface of the joint base 16a, and a substantially flat joint bar 16c which is arranged between the joint base 16a and the joint cover 16b. Further, connected to both ends of the joint bar 16c are a plurality of (e.g., four) lead lines 20 and the joint cable 15 (See FIG. 8), electrical conduction being established between each lead line 20 and the flexible cable (See FIG. 8).
The lead lines 20 are led out to the exterior from one end surface of the inner lead block 16.
The joint cover 16b comprises a cover portion 16d closing the open surface of the joint base 16a, a box portion 16e outwardly protruding from the cover portion 16d, and a pair of flanges 16f provided in the middle section of the opposed side walls of the box portion 16e. Further, a partition 16g is provided in the interior of the box portion 16e, the upper surface of the partition 16g being flush with the upper surface of the box portion 16e. 
The joint base 16a and the joint cover 16b are joined together by an appropriate means such as snap-in engagement to form an integral unit, with the joint bars 16c being accommodated therein.
The inner lead block 16 is accommodated in the accommodating portion 11g of the upper rotor member 11. In this state, the lead lines 20 of the inner lead block 16 are led out to the exterior from the opening 11n, and a part of the upper end surface of the inner lead block 16 is in contact with the upper wall 11p of the accommodating portion 11g. 
The upper surface of the partition 16g and the upper surface of the box portion 16e are substantially flush with the inner wall surface of the small diameter cylindrical portion.
Next, the lower rotor member 12 of the conventional rotary connector 100 will be described.
As shown in FIG. 13, the lower rotor member 12 is formed of a synthetic resin material, molded, of a substantially ring-like configuration, and comprises a first cylindrical portion 12b having a circular center hole 12a at its center, a second cylindrical portion 12c outwardly (downwardly) connected to the first cylindrical portion 12b, and a circular flange 12d outwardly protruding from the upper end portion of the second cylindrical portion 12c. 
Further, the first cylindrical portion 12b is provided with a pair of grooves 12e opposed to each other, and a plurality of (e.g., five) rectangular openings 12f. The upper inner wall 12g of each of the plurality of openings 12f (See FIG. 10) is formed as a plane orthogonal to the axis of the movable member housing. At the open end of the first cylindrical portion 12b, there is formed a substantially annular inclined surface 12h having a predetermined inclination angle.
The first cylindrical portion 12b of the lower rotor member 12 is inserted into the small diameter cylindrical portion 11b of the upper rotor member 11. At this time, the inner upper wall 12g of each hole 12f is in contact with the upper surface 11k of each engagement portion 11h, and the protrusions 11i are arranged in the grooves 12e. In this way, the upper rotor member 11 and the lower rotor member 12 are engaged with each other.
In the movable member housing (composed of the upper rotor member 11, the lower rotor member 12 and the inner lead block 16) of the rotary connector 100, constructed as described above, however, the inner lead block 16 is accommodated in the accommodating portion 11g of the upper In rotor member 11. Thus, if a strong outward tensile force (in the direction of the arrow B: See FIG. 11) is applied to the lead lines 20 of the inner lead block 16 or the inner lead block 16 itself, the accommodating portion 11g is pulled in the direction of the arrow B by this tensile force through the inner lead block 16.
And, when the accommodating portion 11g is pulled, this tensile force is applied to the upper surface 11p of the accommodating portion 11g. To achieve balance in weight of the upper rotor member 11, the upper surface 11p is thin-walled and light in weight, which means it does not have a sufficient strength. Thus, by the force strongly pulling the lead lines 20 or the force upwardly pulling the inner lead block 16, the upper surface 11p is damaged, and the inner lead block 16 is detached from the accommodating portion 11g and gets out of it. Thus, it is not strong enough to withstand decomposition.
The present invention has been made with a view toward solving the above problem in the prior art. It is accordingly an object of the present invention to provide a rotary connector in which the inner lead block 16, accommodated in the accommodating portion 11g of the upper rotor member 11, is reliably kept accommodated in the accommodating portion 11g even if a strong tensile force is applied to the inner lead block 16 and which is strong enough to withstand decomposition.
In accordance with the present invention, there is provided a rotary connector comprising a movable member housing consisting of a lead block having a lock portion, an upper rotor member having an accommodating portion accommodating the lead block and a plurality of engagement portions, and a lower rotor member inserted into the upper rotor member and having a plurality of holding portions to be engaged with the lock portion and the engagement portions, and a stationary member housing supporting the movable member housing, wherein the lower rotor member is inserted into the upper rotor member in which the lead block is accommodated to cause the holding portions to be engaged with the lock portion and the engagement portions.
Further, in accordance with the present invention, there is provided a rotary connector comprising a movable member housing consisting of a lead block having a lock portion, an upper rotor member having an accommodating portion accommodating the lead block and a cylindrical portion equipped with a plurality of engagement portions, and a lower rotor member inserted into the cylindrical portion of the upper rotor member and having a plurality of holding portions to be engaged with the lock portion and the engagement portions, and a stationary member housing supporting the movable member housing, wherein the lead block is accommodated in the accommodating portion, the lock portion being arranged in the cylindrical portion, the lower rotor member being inserted into the cylindrical portion of the upper rotor member to cause the holding portions to be engaged with the lock portion and the engagement portions.
Further, in accordance with the present invention, there is provided a rotary connector wherein the engagement surface between the lock portion and the holding portions is formed so as to make an acute angle with respect to the inner wall of the cylindrical portion of the upper rotor member.
Further, in accordance with the present invention, there is provided a rotary connector wherein the holding portions are provided on the inner wall of a hole provided in the cylindrical portion of the lower rotor member.